The difficulties in diagnosing lameness in heavy horses
For equine vets in general practice one of the most common problems is lameness. Laminitis is very common and is normally seen in both front feet giving the classic stance; where the animal tries to put more weight on the hind legs. There are cases where all four legs are affected but these are less common and very rarely are the hind legs affected without some involvement of the front legs. Even more rarely is just one leg affected with laminitis. This occurs when a horse is non-weight bearing on one leg e.g. from a fracture and then the poor horse gets laminitis in the good leg from the extra use.
Laminitis causes not only is an acute problem but it also leads on to other long-term problems such as seedy toe. This in turn leads to ‘pus in the foot’, which is the most common cause of single leg lameness.
So obviously if foot problems are the most common cause of equine lameness equine vets are going to carefully examine the foot of any lame horse. They will pay particular attention to any pain exhibited when hoot testers are applied. They will also check to see if there are digital pulses. These are not so easy to appreciate in heavy horses on account of their thicker skin. A more pronounced throbbing digital pulse is indicative of ‘pus in the foot’ or laminitis.
Pastern Dermatitis often wrongly called ‘mud fever’ (It can easily occur in dry weather and have nothing to do with mud!), if severe can cause lameness and easily seen by the vet on examination. Equally wounds on any part of the leg may cause lameness either from direct pain when the wounded skin is stretched or from secondary pain caused by infection.
Now we come to the difficult part in heavy horses when there is no obvious cause for the lameness. In riding horses and ponies, vets will get the owner to walk the horse and then to trot the horse in a straight line. They will then grade the lameness with a number out of ten. A ten tenths lame horse will not put its foot to the ground. A one tenth lame horse will only be apparently lame to a vet, a farrier or experienced horse handler. Obviously there are gradations in between these extremes. This assessment is often not easy in heavy horses as they are often reluctant to trot in hand.
The next test which a vet would perform (obviously being mindful of pain), would be to carry out flexion tests on not only the obviously lame limb but also on the other limbs. If flexion makes the lameness worse then that is an indication that either a joint, ligament or tendon is involved. Once again these flexion tests may not be so easy in a heavy horse as not only as stated earlier are they often reluctant to trot but also they may be reluctant to hold their leg flexed for a minimum of 30 seconds to carry out the flexion test.
Having carried out these tests and as a result of these tests a vet would perhaps like the horse lunged in a circle both clockwise and anticlockwise before and after further flexion tests. There are very few heavy horses which would be very helpful to being made to lunge.
In a riding horse or pony a vet might then elect to carry out a systematic series of nerve blocks starting low down on leg to see if pain can be eliminated and therefore the seat of the pain can be determined. This systematic approach relies on consistency which as we have already said would not be easy with a heavy horse. Also the technique of nerve blocking requires accuracy in placing the small amount of local anaesthetic exactly over the nerve. This is much harder in a thick-skin heavy horse.
The temptation for a vet with a lame heavy horse is to skip nerve blocking and go straight to the taking of radiographs. Heavy horses are normally well behaved so that sedation is not required but the difficulty is knowing, which area to radiograph. We are helped at Westover as we have ‘state of the art’ digital x-ray equipment, which makes taking multiple radiographs much easier. However it is vital to be able to assess the clinical finding with the radiological findings. Without nerve blocks this is very difficult.
Heavy horses rarely strain flexor tendons unlike riding horses and particularly race horses. However scanning of tendons even with an up to date scanner is not as easy in heavy horses as not only do they have thick skin but also it is a serious mission to clip the hair off the area to be scanned.
In conclusion diagnosing the cause of lameness, when there is no visible cause, is a diagnostic challenge for the practitioner. The good news in heavy horses is that they are normally kind individuals so that the danger of a nasty kick is much less than with a flighty riding horse or pony.
All I can say is keep bringing lame heavy horses in to us and we will give them our best shot.